Microplastic deformation activating residual stress relief for Al alloy

Abstract

Thermal-vibratory technique has been demonstrated to effectively and rapidly reduce residual stress and improve mechanical properties of materials. But the underlying residual stress relief mechanism remains unclear, limiting the development and application of the technique. In this work, the relationship between residual stress and microstructure evolution during thermal-vibratory process in 7085 Al alloy is systematically investigated, using a combination of experiments, molecular dynamic (MD) simulations, and artificial neural network (ANN). Experimental results show that increasing the thermal-vibratory temperature improves the residual stress relief rate and triggers the uniform distribution of dislocations owing to temperature-enhanced dislocations activity. At the atomic scale, the MD simulation also observed an increasing tendency in residual stress relief rate with increasing temperature. Moreover, MD simulations further reveal that the high shear strain around grain boundaries triggers dislocation motion, accompanied with the decrease of residual stress in the grain interior. That means the residual stress relief is controlled by the dislocation activation around grain boundaries, and the residual stress is relieved only when the material undergoes plastic deformation. Based on the ANN, a map of the residual stress relief rate versus the initial residual stress, thermal-vibratory amplitude, and temperature is constructed, to guide the optimal thermal-vibratory process. These results provide fundamental knowledge and method to determine the residual stress after thermal vibratory treatment, and can further realize the precise control of shape and properties of materials during manufacturing.